1. Field of the Invention
The present invention is related to a portable communication terminal such as a portable telephone which is capable of acquiring positional information by utilizing a positional information system function such as a GPS that can measure a position at the present time, and is also capable of transmitting/receiving the acquired positional information.
2. Description of the Related Art
A portable telephone which is capable of using a positional information system function has already been in actual use. As the positional information system, there is a system in which a present position of a portable telephone is identified on the basis of positions of a plurality of base stations capable of communicating this portable telephone. There is also a GPS (Global Positioning System) capable of positioning the position of a portable telephone based on arrival time differences of electromagnetic waves transmitted from a plurality of satellites.
Users of portable telephones can judge correct positions of the users by using these positional information system functions. Also, a position of a user on the transmission side can be identified even in a portable telephone on the reception side by using the following methods (see, for example, JP-A-2002-335551). That is, in one method, after a portable telephone of the user has acquired positional information, while this user is making a telephone communication with another portable telephone, the acquired positional information is transmitted as partial data of the telephone communication data. In another method, after the telephone communication ends, the positional information is transmitted.
In a case that this portable telephone is lost, this lost portable telephone may be found out in such a way that a telephone communication is made from another portable telephone so as to send positional information, and this sent positional information is used to find out the lost portable telephone.
JP-A-2002-335551 is referred as a related art.
However, the above portable telephone owns the following problem. That is, in a case that a telephone communication is received from a terminal of an ill-intentioned caller and a telephone communication is commenced for the caller's purpose between the portable telephone and the terminal, when the terminal of the ill-intentioned caller transmits to the portable telephone such a signal for requesting sending of positional information, the positional information is freely derived from this portable telephone. Thus, there is a risk that an invasion of a privacy of the user may occur.